Dust suppressing aggregate

ABSTRACT

A dust suppressing aggregate includes a core particle and a dust suppressing agent. The dust suppressing agent comprises polyurethane and is disposed about the core particle for suppressing dusting of the core particle. A method of forming the dust suppressing aggregate includes the steps of providing the core particle and encapsulating the core particle with the polyurethane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Patent Application Nos. 61/648,707, filed on May 18, 2012, 61/648,766, filed on May 18, 2102 and 61/648,884, filed on May 18, 2012, which are incorporated herewith by reference in their entirety.

This application is related to the following U.S. Non-Provisional Patent Application assigned to the same assignee, each of which is incorporated herein by reference in its entirety: U.S. patent application Ser. No. ______, filed on May 17, 2013, entitled “ENCAPSULATED PARTICLE”, claiming priority to U.S. Provisional Patent Application No. 61/648,697, having Attorney Docket No. PF-72188/065322.00185, with Alice Hudson, Lillian Senior, Bernard Sencherey, and Victor Granquist as inventors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention generally relates to a dust suppressing aggregate. More specifically, the subject invention relates to a dust suppressing aggregate that includes a dust suppressing agent disposed about a core particle for suppressing dusting of the core particle.

2. Description of the Related Art

Fertilizers comprising particulate materials tend to generate dust during manufacturing, handling, storage, and application. Dust is generated when the particulate materials break into smaller particles. In particular, fertilizers comprising ammonium phosphates, calcium phosphates, ammonium nitrates, potassium nitrates, potassium chlorides, potassium sulfates, etc. tend to generate substantial levels of undesirable dust.

The generation of dust during manufacturing, handling, storage, and application of fertilizers is problematic for a number of reasons. Typically, dust generated is ultimately wasted, i.e., it does not reach its intended application. The dust generated does, however, typically enter the air and surrounding environs which may cause health and environmental concerns. In an effort to curtail such waste and alleviate such concerns, dust suppressants are often applied to fertilizers to reduce the generation of dust.

Dust suppressants are typically liquids, such as oils, but can be solids, such as waxes. Particular examples of dust suppressants are petroleum residue, hydrogenated mineral oil, and wax. Dust suppressants are typically spray applied onto the fertilizer. The spray application of the dust suppressant onto the fertilizer typically occurs in combination with agitation in a rotating drum or tumbler. The agitation facilitates coverage of the dust suppressant onto the fertilizer, i.e., onto the surface of the particulate materials.

To date, treatment of fertilizers has focused on dust suppressants such as mineral oils and waxes. There are disadvantages associated with such dust suppressants. Liquid dust suppressants, such as mineral oils, may volatilize and/or migrate into the fertilizer with time and lose their effectiveness. Solid dust suppressants, such as waxes, can be difficult to handle, require special application equipment, cause clumping or agglomeration, and can inhibit the dissolution/release of the fertilizer once applied.

Accordingly, there remains a need to develop an improved dust suppressing agent.

SUMMARY OF THE INVENTION AND ADVANTAGES

The invention provides dust suppressing aggregate including a core particle and a dust suppressing agent. The dust suppressing agent comprises polyurethane and is disposed about the core particle for suppressing dusting of the core particle. A method of forming the dust suppressing aggregate includes the steps of providing the core particle and encapsulating the core particle with the polyurethane.

The polyurethane protects the core particle and minimizes the generation of dust by the core particle. The polyurethane is solid, does not volatilize and/or migrate into the fertilizer with time and lose its effectiveness as a dust suppressant. Further, the polyol and isocyanate components from which the polyurethane is formed promote consistent and minimal encapsulation of the core particle by the polyurethane and form the polyurethane which is durable and prevents clumping and agglomeration of the core particles. Although the polyurethane serves to protect the core particle and prevent the generation of dust, the polyurethane allows for the rapid permeation of water and does not significantly inhibit the dissolution/release of the core particle.

DETAILED DESCRIPTION

The instant invention provides a dust suppressing aggregate. The dust suppressing aggregate includes a core particle and a dust suppressing agent. The dust suppressing aggregate is typically free of liquid dust suppressants. The core particle typically includes a fertilizer that may include calcium, magnesium, nitrogen, phosphate, potassium, sulfur, and combinations thereof. The fertilizer may be selected from the group of nitrogenous fertilizers, phosphoric fertilizers, potash fertilizers, sulfuric fertilizers, and combinations thereof, e.g. mixed fertilizers. Suitable fertilizers include, but are not limited to, anhydrous ammonia, urea, ammonium nitrate, urea ammonium nitrate, potassium nitrate, calcium ammonium nitrate, calcium phosphate, phosphoric acid, monoammonium phosphate, ammonium polyphosphate, ammonium phosphate sulfate, potash, ammonium nitrate, potassium nitrate, potassium chloride, potassium sulfate, ammonium sulfate and sulfuric acid, and combinations thereof. Typical non-limiting examples of fertilizer include urea and monoammonium phosphate.

The core particle may also include herbicides, insecticides, fungicides, and other components for use in agricultural applications. However, the dust suppressing aggregate is not limited for use in agricultural applications and the core particle of the present invention is not limited to the components described immediately above.

Although the shape of the core particle is not critical, core particles having a spherical shape are preferred. Accordingly, the core particle is typically either round or roughly spherical. Although the core particle may be of any size, the core particle typically has a particle size of from No. 170 to 5/16 in., more typically from No. 35 to No. 3½, and most typically from No. 18 to No. 5, mesh, as measured in accordance with standard sizing techniques using the United States Sieve Series. That is, the core particle typically has a particle size of from 0.1 to 7, more typically from 0.5 to 5, and most typically from 1 to 4, mm. Core particles which are round or roughly spherical and have such particle sizes typically allow less dust suppressing agent to be used and typically allow the dust suppressing agent to be disposed on the core particle with increased uniformity and completeness as compared to core particles having other particle shapes and sizes.

The dust suppressing agent comprises polyurethane and is disposed about the core particle for suppressing dusting of the core particle. The polyurethane may be partially or completely disposed about the core particle. The polyurethane comprises the reaction product of an isocyanate component and a polyol component.

The isocyanate component typically includes an aromatic isocyanate. More typically, the isocyanate component includes, but is not limited to, monomeric and polymeric methylene diphenyl diisocyanate, monomeric and polymeric toluene diisocyanate, and mixtures thereof. Most typically, the isocyanate component is LUPRANATE® M20 commercially available from BASF Corporation of Florham Park, N.J.

LUPRANATE® M20 comprises polymeric diphenylmethane diisocyanate and has an NCO content of about 31.5 weight percent. Polymeric methylene diphenyl diisocyanates such as LUPRANATE® M20 offer high crosslink density and moderate viscosity. Alternatively, monomeric methylene diphenyl diisocyanates such as LUPRANATE® M offer low viscosity and high NCO content with low nominal functionality. Similarly, toluene diisocyanates such as LUPRANATE® TDI also offer low viscosity and high NCO content with low nominal functionality.

Typically, the isocyanate component has a viscosity of from 1 to 3000, more typically from 20 to 700, and most typically from 50 to 300, centipoise at 25° C. The most typical viscosity of the isocyanate component is from 50 to 300 centipoise at 25° C. to allow the isocyanate component to be sprayed onto the core particle. Typically, the isocyanate component has a nominal functionality from 1 to 5, more typically from 1.5 to 4, and most typically from 2.0 to 2.7. The most typical nominal functionality of the isocyanate component is from 2.0 to 2.7 to allow for effective reaction of the isocyanate component with the polyol component and for cost effectiveness. Typically, the isocyanate component has an NCO content of from 20 to 50, more typically from 25 to 40, and most typically from 30 to 34, % by weight. The NCO content provides a high molecular crosslink density that aids in the formation of the polyurethane. The NCO content also provides more chemical bonds per unit of mass to improve cost efficiency. The viscosity, the nominal functionality, and the NCO content of the isocyanate component may vary outside of the ranges above, but are typically both whole and fractional values within those ranges.

Referring back to the polyol component, the polyol component typically includes one or more polyols having one or more OH functional groups, typically at least two OH functional groups. In addition to, or in lieu of, the OH functional group(s), the polyol component can include isocyanate-reactive moieties having one or more NH functional groups. Typically, the polyol component includes one or more polyols selected from the group of polyether polyols, polyester polyols, polyether/ester polyols, and combinations thereof. However, other polyols may also be employed.

In one embodiment, the polyol component includes a high-molecular weight (HMW) polyol. The HMW polyol is typically a high molecular weight, primary hydroxyl terminated polyol. The HMW polyol is typically initiated with at least one non-amine based, tri-functional initiator. Suitable initiators for initiating the HMW polyol include, but are not limited to, glycerine, trimethylolpropane, propylene glycol, dipropylene glycol, isopropylene glocol, sorbitol, sucrose, and the like.

The HMW polyol has a number average molecular weight, of greater than 1400 g/mol because such a number average molecular weight, tends to improve performance properties of the polyurethane. This number average molecular weight, tends to impart elasticity, abrasion resistance, and controlled release properties to the polyurethane. Typically, the HMW polyol has a number average molecular weight, of greater than 400, more typically from 400 to 15000, and most typically from 500 to 7000, g/mol. Typically, the HMW polyol has a viscosity of from 100 to 2000, more typically from 150 to 1800, and most typically from 200 to 1600, centipoise at 25° C. Typically, the HMW polyol has a nominal functionality of at least 1.6, more typically from 1.8 to 5, and most typically from 1.8 to 3.2. Typically, the HMW polyol has an OH number of from 20 to 300, more typically from 23 to 275, and most typically from 25 to 250, mg KOH/g. The number average molecular weight, viscosity, nominal functionality, and OH number of the HMW polyol may be any value outside of the ranges above, but are typically both whole and fractional values within those ranges. Non-limiting examples of a typical HMW polyol include PLURACOL® 220, PLURACOL® 2010, and PLURACOL® 4156, all commercially available from BASF Corporation of Florham Park, N.J.

The polyol component can also include the catalytic polyol. The catalytic polyol is different from the HMW polyol. The catalytic polyol is referred to as a “catalytic” polyol because the catalytic polyol can be used instead of a catalyst to facilitate the chemical reaction of the isocyanate component with the polyol component. Said differently, a polyol component that includes the catalytic polyol will typically chemically react with the isocyanate component at lower temperatures in the presence of less catalyst (even no catalyst) than a polyol component that does not include the catalytic polyol. The catalytic polyol is typically derived from an amine-based initiator. The catalytic polyol may be formed with more than one initiator. In one embodiment, the catalytic polyol is derived from a dipropylene glycol initiator. In another embodiment, the catalytic polyol may be co-initiated with dipropylene glycol. Without being bound by theory, it is believed that amine content of the catalytic polyol facilitates the reaction of the isocyanate component with the polyol component.

The catalytic polyol may also include alkylene oxide substituents. Examples of suitable alkylene oxides substituents include ethylene oxide, propylene oxide, butylene oxide, amylene oxide, mixtures thereof, alkylene oxide-tetrahydrofuran mixtures, epihalohydrins, and aralkylene styrene.

One embodiment of the catalytic polyol that is formed from an amine-based initiator typically has a viscosity of from 500 to 75,000, more typically from 32,000 to 72,000, and most typically from 42,000 to 62,000 centipoise at 25° C.; a nominal functionality typically greater than 2.5, more typically of from 2.75 to 10, and most typically from 3 to 4; an OH number of from 200 to 950, more typically from 250 to 850, and most typically from 750 to 800, mg KOH/g; and a number average molecular weight of less than 1400, more typically from 100 to 1120, and most typically from 192 to 392, g/mol. The viscosity, nominal functionality, OH number, and number average molecular weight of the catalytic polyol of this embodiment may vary outside of the ranges above, but are typically both whole and fractional values within those ranges. One example of a suitable catalytic polyol of this embodiment is commercially available from BASF Corporation of Florham Park, N.J. under the trade name of QUADROL®.

Another embodiment of the catalytic polyol is formed from an aromatic amine-based initiator. The aromatic amine-based initiator is of the formula:

wherein R₁ includes one of an alkyl group, an amine group, and a hydrogen and each of R₂-R₆ independently include one of an amine group and a hydrogen, so long as at least one of R₁-R₆ is an amine group. Therefore, it is to be understood that R₁ can be any one of an alkyl group, an amine group, or a hydrogen, or any compound including combinations thereof. It is also to be understood that R₂-R₆ do not have to be identical and each can include an amine group or a hydrogen. It is also to be understood that the terminology “an amine group” refers to R—N—H and NH₂ throughout.

The aromatic amine-based initiator may include, but is not limited to, a toluene diamine. The toluene diamine typically includes, but is not limited to, the following structures:

wherein the toluene diamine includes, but is not limited to, 2,3-toluenediamine, 2,4-toluenediamine, 2,5-toluenediamine, 2,6-toluenediamine, 3,4-toluenediamine, 3,5-toluenediamine, and mixtures thereof.

The aromatic amine-based initiator tends to yield a catalytic polyol that is miscible with the isocyanate component, e.g. completely miscible. The miscibility of the isocyanate component and the catalytic polyol that is derived from an aromatic amine-based initiator tends to result from two primary effects. First, the miscibility is affected by London Forces that create momentarily induced dipoles between similar aromatic moieties of the catalytic polyol and the isocyanate component. The momentarily induced dipoles allow the catalytic polyol and the isocyanate component to mix effectively. Secondly, the miscibility is affected by the planar geometry of the aromatic moieties of the catalytic polyol and the isocyanate component that allow for complementary stacking of the catalytic polyol and isocyanate component. As such, the isocyanate component and the polyol component mix effectively.

The embodiment of the catalytic polyol formed from an aromatic amine-based initiator typically has a viscosity of from 400 to 100,000, more typically from 450 to 10,000, and most typically from 500 to 2500, centipoise at 25° C.; a nominal functionality typically greater than 2.5, more typically from 2.75 to 10, and most typically from 3 to 4; an OH number of from 200 to 950, more typically from 250 to 850, and most typically from 750 to 800, mg KOH/g; and a number average molecular weight of less than 1400, more typically from 100 to 1120, and most typically from 639 to 839, g/mol. The viscosity, nominal functionality, OH number, and number average molecular weight of the catalytic polyol of this embodiment may vary outside of the ranges above, but are typically both whole and fractional values within those ranges. Examples of suitable catalytic polyols of this embodiment are commercially available from BASF Corporation of Florham Park, N.J. under the trade names of PLURACOL® 1168 and PLURACOL® 1578.

If present, the catalytic polyol is typically present in the polyol component in an amount of from 1 to 95, more typically in an amount from to 65, and most typically in an amount from 15 to 35, parts by weight based on 100 parts by weight of the polyol component. The amount of the catalytic polyol may vary outside of the ranges above, but is typically both whole and fractional values within those ranges.

If the HMW and the catalytic polyol are both present in the polyol component, the catalytic polyol is typically present in the polyol component in an amount which is less than the amount of the HMW polyol. A weight ratio of the HMW polyol to the catalytic polyol in the polyol component is typically of from 1:1 to 15:1, more typically from 2:1 to 12:1, and most typically from 2.5:1 to 10:1. The weight ratio of the HMW polyol to the catalytic polyol may vary outside of the ranges above, but is typically both whole and fractional values within those ranges.

The polyurethane can be formed in the presence of a silicone surfactant. The silicone surfactant is typically a polyorganosiloxane. A non-limiting example of a typical polyorganosiloxane is an alkyl pendent organosilicone molecule comprising a polysiloxane backbone and polyether side chains. The alkyl pendent organosilicone molecule of this example can be comb structured or dendrimer structured.

The silicone surfactant typically improves the wetting of the polyol component and the isocyanate component on the core particle and, accordingly, may also be described as a wetting agent. The silicone surfactant also typically improves the adhesion of the polyurethane to the core particle. In addition, the silicone surfactant reduces clumping and agglomeration of the dust suppressing aggregate during and after the encapsulation process. As such, the silicone surfactant promotes more complete encapsulation of the core particle by the polyurethane, promotes consistent thickness of the polyurethane, allows for formation of the polyurethane having minimal but consistent thickness, reduces the amount of the polyurethane that is required to coat the core particle thereby decreasing the amount of the isocyanate component and the polyol component collectively required to encapsulate the core particles with a consistently thick coating of the polyurethane, increases a yield of dust suppressing aggregates encapsulated with a consistent coating of the polyurethane, and minimizes pits and depressions in the polyurethane. Typically, the silicone surfactant is a liquid and has a viscosity of from 100 to 1500, more typically from 200 to 1000, and most typically from 650 to 850, cSt at 25° C. The viscosity of the silicone surfactant may vary outside of the ranges above, but is typically both whole and fractional values within those ranges.

Specific examples of suitable silicone surfactants include, but are not limited to, TEGOSTAB® BF 2370, commercially available from Goldschmidt AG of Essen, Del., DABCO® DC5043 commercially available from Air Products and Chemicals, Inc. of Allentown, Pa., and NIAX® Silicone L-5340 and L-620, both commercially available from Momentive Performance Materials of Albany, N.Y. A particularly suitable silicone surfactant is NIAX® Silicone L-620, a polyalkyleneoxidemethylsiloxane copolymer. The silicone surfactant may be present in the polyol component in an amount of from 0.01 to 10, typically from 0.05 to 5, and more typically from 0.5 to 1.5, parts by weight based on 100 parts by weight of all components used to form the polyurethane. The parts by weight silicone surfactant may vary outside of the ranges above, but is typically both whole and fractional values within those ranges.

The polyurethane may optionally include one or more additives. The additives are typically included in polyol component, but can be included in the isocyanate component or added separately. Suitable additives for purposes of the present invention include, but are not limited to, chain-extenders, cross-linkers, chain-terminators, processing additives, adhesion promoters, anti-oxidants, defoamers, flame retardants, catalysts, anti-foaming agents, water scavengers, molecular sieves, fumed silicas, surfactants, ultraviolet light stabilizers, fillers, thixotropic agents, silicones, colorants, pigments, inert diluents, and combinations thereof. For example, a pigment can be included in the polyurethane. If included, the additives can be included in the polyurethane in various amounts.

The dust suppressing agent comprising polyurethane is typically present in the dust suppressing aggregate in an amount of from 0.3 to 5.5, more typically from 0.5 to 3.0, and most typically from 0.7 to 2.0, parts by weight based on 100 parts by weight of the core particle. The amount of dust suppressing agent comprising polyurethane present in the dust suppressing aggregate may vary outside of the ranges above, but is typically both whole and fractional values within those ranges.

The dust suppressing aggregate, including the core particle and the polyurethane thereon, is typically either round or roughly spherical. The dust suppressing aggregates have a size distribution reported as D[4,3], d(0.1), d(0.5), and/or d(0.9), as well defined and appreciated in the art. In several embodiments, the dust suppressing aggregates have a size distribution D[4,3] of from 0.5 to 5 mm, of from 1 to 4 mm, or of from 1 to 3 mm, with an overall particle size range of from 0.1 to mm. In other embodiments, the dust suppressing aggregates have a size distribution d(0.1) of from 0.2 to 2 mm, of from 0.4 to 1.7 mm, or of from 0.5 to 1.5 mm, with an overall particle size range of from 0.1 to 10 mm. In further embodiments, the dust suppressing aggregates have a size distribution d(0.5) of from 0.5 to 5 mm, of from 1 to 4 mm, or of from 1 to 3 mm, with an overall particle size range of from 0.1 to mm. In still other embodiments, the dust suppressing aggregates have a size distribution d(0.9) of from 0.7 to 7 mm, of from 0.8 to 5 mm, or of from 1 to 4 mm, with an overall particle size range of from 0.1 to 10 mm. The D[4,3], d(0.1), d(0.5), and d(0.9) size distributions of the dust suppressing aggregates may vary outside of the ranges above, but are typically both whole and fractional values within 0.5 to 5 mm, 0.2 to 2 mm, 0.5 to 5 mm, and 0.7 to 7 mm, respectively.

The dust suppressing performance of the dust suppressing agent can be determined. To test the dust suppressing performance of the dust suppressing agent, a dust value (ppm) of the dust suppressing aggregate is determined. Dust value is measured by placing a 50 g sample of the dust suppressing aggregate in a 125 mL wide mouth glass jar. The jar is placed in a Burrell Model 75 wrist-action shaker, and shaken for 20 minutes at the maximum intensity setting (10). After shaking, the sample is weighed and then processed in a dust removal apparatus. The dust removal apparatus consists of a 2.5 in. diameter plastic cup, a cup holder, an air flow meter, and a vacuum cleaner. The base of the cup is removed and replaced with a 200 mesh screen. Each sample is placed into the cup, the cup is placed into the holder, and then air is drawn through the sample for two minutes at a rate of 9 standard cubic feet per minute using the vacuum cleaner. The sample is then re-weighed. The amount of dust is calculated from the weight difference before and after dust removal. Results are reported as an average of two replicates.

Typically, the dust suppressing aggregate has a dust value of less than 3000, more typically less than 2000, still more typically less than 1000, even more typically less than 500, and most typically less than 250, ppm.

In one embodiment, the dust suppressing aggregate comprises the dust suppressing agent in an amount no greater than 1 part by weight based on 100 parts by weight of the dust suppressing aggregate and has an initial dust value of less than 1000, more typically less than 750, and most typically less than 500, ppm.

In another embodiment, the dust suppressing aggregate comprises the dust suppressing agent in an amount no greater than 2 parts by weight based on 100 parts by weight of the dust suppressing aggregate and has an initial dust value of less than 500, more typically less than 200, and most typically less than 150, ppm.

A dust reduction gradient (%) can be determined with the dust value. The dust reduction gradient is calculated with the following formula:

[(Dust Value A−Dust Value B)/Dust Value A]×100

Dust Value A is the dust value of the uncoated core particle

Dust Value B is the dust value of the dust suppressing aggregate comprising an identical core particle.

Said differently, once the dust value for the uncoated core particle and dust suppressing aggregate are determined under certain conditions, the dust reduction gradient (%) is the percent difference in the amount of dust generated by the uncoated core particle and the coated core particle, i.e., the dust suppressing aggregate. Typically, the larger the dust reduction gradient, the better. In one embodiment, the dust suppressing aggregate comprises the dust suppressing agent in an amount no greater than 1 part by weight based on 100 parts by weight of the dust suppressing aggregate and has an initial dust reduction gradient of greater than 10, more typically greater than 50, and most typically greater than 80, %.

In another embodiment, the dust suppressing aggregate comprises the dust suppressing agent in an amount no greater than 2 parts by weight based on 100 parts by weight of the dust suppressing aggregate and has an initial dust reduction gradient of greater than 20, more typically greater than 60, and most typically greater than 90, %.

The polyurethane of the dust suppressing aggregate has minimal impact dissolution of the core particle. That is, the dust suppressing agent comprising polyurethane minimally impacts the rate at which the core particle dissolves. Dissolution is the amount of core particle that dissolves in water under certain conditions and is typically measured in weight percent, as is described in greater detail immediately below.

Dissolution is measured by placing 50 g of the dust suppressing aggregate in a 250 mL plastic bottle. Then 230 g of deionized water is added to the bottle. The plastic bottle is allowed to stand undisturbed for 8 hours at room temperature (23° C.). A liquid sample is then drawn, and its refractive index is measured using a refractometer. An amount (in grams) of the core particle dissolved in each solution sample is calculated using the refractive index and a temperature-corrected standard curve. The amount of the core particle dissolved is utilized to calculate dissolution (%) with the following formula:

Dissolution (%)=X/(50−(Weight Percent Dust Suppressing Agent Applied/2))

X=the amount of core particle (grams) dissolved in the solution sample.

Weight Percent Dust Suppressing Agent Applied=100%×Dust Suppressing Agent Applied/Weight of Dust Suppressing Aggregate

A dissolution gradient can be determined with the dissolution. The dissolution gradient is simply the difference in the dissolution (%) of the uncoated core particle and the dissolution of the core particle of the dust suppressing aggregate. Said differently, once the dissolution for the uncoated core particle and the dust suppressing aggregate are determined under certain conditions, the dissolution gradient is absolute value of the dissolution of the uncoated core particle minus the dissolution of the dust suppressing aggregate. Typically, the smaller the dissolution gradient, the better. Although the dust suppressing agent should inhibit dusting of the core particle, it is typically desired that the dust suppressing agent minimally impact the dissolution of the core particle. Typically, the dust suppressing aggregate has a dissolution gradient equal to or less than 30, more typically less than 15, still more typically less than 10, and most typically less than 5 after 1 day of aging in water at 23° C.

In addition to the dust suppressing aggregate, the subject invention relates to a system for forming the dust suppressing aggregate and a method of forming the dust suppressing aggregate. The system for forming the dust suppressing aggregate includes the isocyanate component, the polyol component, and the core particle.

The method includes the steps of providing the core particle and encapsulating the core particle with the polyurethane. The step of encapsulating the core particle with the polyurethane can be further defined as reacting the isocyanate component and the polyol component to form the polyurethane. Typically, the isocyanate component and the polyol component are mixed, i.e. combined, and chemically react to form the polyurethane. Typically, the isocyanate component and the polyol component are reacted at an isocyanate index of from 90 to 160, more typically from 110 to 140, and most typically from 125 to 135. As well known in the art, isocyanate index is a ratio of an actual molar amount of isocyanate(s) reacted with the polyol(s) to a stoiciometric molar amount of isocyanate(s) needed to react with an equivalent molar amount of the polyol(s). The step of reacting the isocyanate component and the polyol component can be conducted prior to the step of encapsulating the core particle with the polyurethane. Alternatively, the step of reacting the isocyanate component and the polyol component can be conducted simultaneous with the step of encapsulating the core particle with the polyurethane.

The isocyanate component and the polyol component may be combined using one or more techniques including, but not limited to, pouring, pan coating, fluidized-bed coating, co-extrusion, mixing, spraying and spinning disk encapsulation. Most typically, the isocyanate component and the polyol component are mixed by spraying into or above the reaction vessel such as a barrel, a drum, mixer, or the like. The polyol component and the isocyanate component can be mixed and sprayed into or above the reaction vessel with a single spray gun or multiple spray guns. In one embodiment, the isocyanate component and the polyol component are impingement mixed in a spray nozzle. The polyol component and the isocyanate component can also be sequentially sprayed into or above the reaction vessel with a single spray gun and mixed in the reaction vessel. Alternatively, the isocyanate component and the polyol component can be simultaneously or sequentially sprayed into or above the reaction vessel with different spay guns.

As just one non-limiting example, the isocyanate component and the polyol component can be sprayed onto the core particle in the following sequence: (1) a portion of the isocyanate component is sprayed onto the core particle; (2) a portion of the of the polyol component is sprayed onto the core particle; (3) a remaining portion of the isocyanate component is sprayed onto the core particle; and, (4) a remaining portion of the polyol component is sprayed onto the core particle. As another non-limiting example, the isocyanate component and the polyol component can be sprayed onto the core particle in the following sequence: (1) a portion of the isocyanate component is sprayed onto the core particle; (2) a portion of the of the polyol component is sprayed onto the core particle and a remaining portion of the isocyanate component is sprayed onto the core particle simultaneously; and, (3) a remaining portion of the polyol component is sprayed onto the core particle.

The method optionally includes the step(s) of heating the isocyanate component, the polyol component, and/or the core particles prior to, or simultaneous with, the step of mixing the isocyanate component and the polyol component. The isocyanate component, the polyol component, the silicone surfactant, and/or the core particles may be individually heated or heated in combination with one or more of each other. The isocyanate component, the polyol component, and the core particle are typically heated prior to or simultaneous with the step of encapsulating the core particle. Typically, the isocyanate component, the polyol component, and the core particle are heated to a temperature of greater than 40, more typically to a temperature of from 45 to 90, and most typically from 50 to 80, ° C.

The step of encapsulation can occur once or can be repeated. If repeated the step does not have to be the same each individual time. The core particle may be encapsulated one time with the polyurethane or multiple times with the polyurethane. It is contemplated that the core particle can be encapsulated with the polyurethane and one or more additional dust suppressing agents. The core particle may be partially or totally encapsulated.

The following examples illustrate the nature of the invention and are not to be construed as limiting of the invention.

EXAMPLES

Example Dust Suppressing Aggregates (Examples) A-D are described herein. Examples A-D include a core particle and a dust suppressing agent comprising polyurethane disposed about the core particle. Examples A-D are formed in accordance with the present invention.

To form Examples A-D, a dust suppressing agent comprising polyurethane is disposed about a core particle. The compositions used to form Examples A-D, in grams, are set forth below in Table 1. Polyol A is pre-heated to a temperature of 150° F. in a first vessel. Isocyanate is pre-heated to a temperature of 150° F. in a second vessel. Core Particle A is pre-heated to a temperature of 150° F. in a third vessel. Once pre-heated, the Core Particle A is added to a reaction vessel having a roller speed of 26 rpm. Once the Core Particle A is added, the Isocyanate is added to the reaction vessel and agitated for 2 minutes with the Core Particle A. Next, the Polyol A is added to the reaction vessel and agitated with the Isocyanate and the Core Particle A for 10 more minutes. During agitation, the Polyol A and the Isocyanate react to form the dust suppressing agent comprising polyurethane and disposed about the Core Particle A.

TABLE 1 Comparative Core Particle Example A Example B Example C Example D Polyol A — 24.5 27.0 16.3 18 Isocyanate — 5.5 3.0 3.7 2 Core Particle A 2000 2000 2000 2000 2000 Total 2000 2030 2030 2020 2020 Isocyanate — 170 85 170 85 Index Weight Percent   0 1.5 1.5 1 1 Dust Suppressing Agent Applied (%) Polyol A is PLURACOL ® 4156, a high molecular weight polyol commercially available from BASF Corporation of Florham Park, NJ. Isocyanate is LUPRANATE ® M20, a polymeric methylene diphenyl diisocyanate commercially available from BASF Corporation of Florham Park, NJ. Core Particle A is MicroEssentials MES-z, a fertilizer commercially available from Mosaic of Plymouth, MN.

The dust suppressing agent comprising polyurethane of Examples A-D encapsulates the Core Particle A and prevents dust formation upon mechanical abrasion. Further, the dust suppressing agent comprising polyurethane does not significantly inhibit or prevent the dissolution of the Core Particle A.

Example Dust Suppressing Aggregates (Examples) E-U are also described herein. Examples E-U include a core particle and a dust suppressing agent comprising polyurethane disposed about the core particle. Examples E-U are formed in accordance with the present invention.

To form Examples E-U, a dust suppressing agent comprising polyurethane is disposed about a Core Particle. The compositions used to form Examples E-U, in grams, are set forth below in Tables 2 and 3. One or more polyols and additives are mixed to form a polyol component and pre-heated to a temperature of 150° F. in a first vessel. Isocyanate is pre-heated to a temperature of 150° F. in a second vessel. Core Particle A or B (depending on the Example) is pre-heated to a temperature of 150° F. in a third vessel. Once pre-heated, the Core Particle A or B is added to a reaction vessel having a roller speed of 26 rpm. Once the Core Particle A or B is added, the Isocyanate is added to the reaction vessel and agitated for 2 minutes with the Core Particle A or B. Next, the polyol component is added to the reaction vessel and agitated with the Isocyanate and the Core Particle A or B for 10 more minutes. During agitation, the polyol component and the Isocyanate react to form the dust suppressing agent comprising polyurethane and disposed about the Core Particle.

TABLE 2 Ex. E Ex. F Ex. G Ex. H Ex. I Ex. J Ex. K Ex. L Ex. M Polyol A — — — — — — — 16.91 32.81 Polyol B .38 .76 .76 11.37 18.42 11.51 5.75 5.47 10.94 Polyol C 1.14 2.27 2.27 34.11 — 34.53 17.26 — — Polyol D — — — — 55.27 — — — — Additive A .01 .02 .02 .27 .44 — — — — Additive B .02 .03 .03 .45 .74 — — — — Additive C .02 .03 .03 .45 .74 0.46 .23 .22 .44 Isocyanate 0.44 .89 .89 13.34 44.39 13.5 6.75 7.91 15.81 Core 200 200 200 3000 — 3000 3000 3000 3000 Particle A Core — — — — 3000 — — — — Particle B Total 202 204 204 3060 3120 3060 3030 3031 3060 Isocyanate 130 130 130 130 130 130 130 130 130 Index Weight 1 2 2 2 4 2 1 1 2 Percent Dust Suppressing Agent Applied (%)

TABLE 3 Ex. N Ex. O Ex. P Ex. Q Ex. R Ex. S Ex. T Ex. U Polyol A 2.19 3.38 3.41 — — — — — Polyol B .73 — — — — — — — Polyol C — — — — — — — — Polyol E — — — 3.68 — — — — Polyol F — — — — 1.79 — — — Polyol G — — — — — 3.54 — — Polyol H — — — — — — 1.34 1.11 Additive C .03 .03 — — — — — — Isocyanate 1.05 0.58 0.59 0.32 2.21 0.46 2.66 2.89 Core Particle 400 400 400 400 400 400 400 400 A Total 404 404 404 404 404 404 404 404 Isocyanate 130 130 130 130 130 130 130 130 Index Weight 1 1 1 1 1 1 1 1 Percent Dust Suppressing Agent Applied (%) Polyol B is PLURACOL ® 1168, an aromatic amine-initiated polyol commercially available from BASF Corporation of Florham Park, NJ. Polyol C is PLURACOL ® 220, a high molecular weight polyol commercially available from BASF Corporation of Florham Park, NJ. Polyol D is castor oil. Polyol E is PLURACOL ® 4650, an aromatic amine-initiated polyol commercially available from BASF Corporation of Florham Park, NJ. Polyol F is PLURACOL ® GP430, an aromatic amine-initiated polyol commercially available from BASF Corporation of Florham Park, NJ. Polyol G is PLURACOL ® 593, an aromatic amine-initiated polyol commercially available from BASF Corporation of Florham Park, NJ. Polyol H is dipropylene glycol. Additive A is ANTIFOAM A, an anti-foaming additive commercially available from Dow Corning Corporation of Midland, MI. Additive B is MOLSIV 3A, molecular sieves commercially available from UOP of Des Plaines, IL. Additive C is NIAX ® L-620, a silicone surfactant commercially available from Momentive Performance Materials of Albany, NY. Isocyanate is LUPRANATE ® M20, a polymeric methylene diphenyl diisocyanate commercially available from BASF Corporation of Florham Park, NJ. Core Particle B is urea granules.

The dust suppressing agent comprising polyurethane of Examples E-U encapsulates the Core Particle A and prevents dust formation upon mechanical abrasion. Further, the dust suppressing agent comprising polyurethane does not significantly inhibit or prevent the dissolution of the Core Particle B.

Example Dust Suppressing Aggregates (Examples) V-X and Comparative Example A are described herein. Examples V-X include a core particle and a dust suppressing agent comprising polyurethane disposed about the core particle. Examples V-X are formed in accordance with the present invention. Comparative Example A is not formed in accordance with the present invention and is included for comparative purposes.

To form Examples V-X, a dust suppressing agent comprising polyurethane is disposed about a Core Particle. The compositions used to form Examples V-X, in grams, are set forth below in Table 4. One or more polyols and additives are mixed to form a polyol component and pre-heated to a temperature of 150° F. in a first vessel. Isocyanate is pre-heated to a temperature of 150° F. in a second vessel. Core Particle B is pre-heated to a temperature of 150° F. in a third vessel. Once pre-heated, the Core Particle B is added to a reaction vessel having a roller speed of 26 rpm. Once the Core Particle B is added, the Isocyanate is added to the reaction vessel and agitated for 2 minutes with the Core Particle B. Next, the polyol component is added to the reaction vessel and agitated with the Isocyanate and the Core Particle B for 10 more minutes. During agitation, the polyol component and the Isocyanate react to form the dust suppressing agent comprising polyurethane and disposed about the Core Particle B.

TABLE 4 Comparative Example Example Example A V W Example X Polyol A — 24.5 48.9 7.8 Polyol I — — — 7.8 Isocyanate — 5.5 11.5 14.5 Core Particle B 3000 3000 3000 3000 Weight Percent 0 1 2 1 Dust Suppressing Agent Applied (%) Dust Value 877 210 150 500 (ppm) Dust Reduction NA 76.1 82.9 43.0 Gradient (%) Dissolution (%) 60.4 70.7 57.8 66.5 (8 hours at 23° C.) Dissolution NA 10.3 2.6 6.1 Gradient *Polyol B is PLURACOL ® 1168, an aromatic amine-initiated polyol commercially available from BASF Corporation of Florham Park, NJ. Core Particle B is SGN 250 (granular urea), a fertilizer commercially available from CF Industries of Deerfield, IL. The urea granules are sifted with US #5 and US #16 sieves to control particle size prior to use.

Dust value (ppm) is measured by placing 50 g sample of each Example dust suppressing aggregate in a 125 mL wide mouth glass jar. The jar is placed in a Burrell Model 75 wrist-action shaker, and shaken for 20 minutes at the maximum intensity setting (10). After shaking, the sample is weighed and then processed in a dust removal apparatus. The dust removal apparatus consists of a 2.5 in. diameter plastic cup, a cup holder, an air flow meter, and a vacuum cleaner. The base of the cup is removed and replaced with a 200 mesh screen. Each sample is placed into the cup, the cup is placed into the holder, and then air is drawn through the sample for two minutes at a rate of 9 standard cubic feet per minute using the vacuum cleaner. The sample is then re-weighed. The amount of dust is calculated from the weight difference before and after dust removal. Results are reported as an average of two replicates.

A dust reduction gradient (%) is determined with the dust value. The dust reduction gradient is calculated with the following formula:

-   [(Dust Value A—Dust Value B)/Dust Value A]×100

Dust Value A is the dust value of the uncoated core particle

Dust Value B is the dust value of the dust suppressing aggregate comprising an identical core particle.

Dissolution (%) is measured by placing 50 g sample of each Example dust suppressing aggregate in a 250 mL plastic bottle. Then 230 g of deionized water is added to the bottle. The plastic bottle is allowed to stand undisturbed for 8 hours at room temperature (23° C.). A liquid sample is then drawn, and its refractive index is measured using a refractometer. An amount (in grams) of the core particle dissolved in each solution sample is calculated using the refractive index and a temperature-corrected standard curve. The amount of the core particle dissolved is utilized to calculate dissolution (%) (e.g. percent urea dissolved) with the following formula:

Dissolution (%)=X/(50−(Weight Percent Dust Suppressing Agent Applied/2))

X=the amount of core particle (grams) dissolved in the solution sample.

% Coating=100%×Dust Suppressing Agent Applied/Weight of Dust Suppressing Aggregate

A dissolution gradient is determined with the dissolution (%). The dissolution gradient is simply the difference in the dissolution (%) of the uncoated core particle and the dissolution of the core particle of the dust suppressing aggregate. Said differently, once the dissolution for the uncoated core particle and the dust suppressing aggregate are determined under certain conditions, the dissolution gradient is absolute value of the dissolution (%) of the uncoated core particle minus the dissolution of the dust suppressing aggregate. Typically, the smaller the dissolution gradient, the better. Although the dust suppressing agent should inhibit dusting of the core particle, it is typically desired that the dust suppressing agent minimally impact the dissolution of the core particle.

Referring now to Table 4, the dust values of Examples V-X are substantially lower than the dust values of the Comparative Example A (uncoated Core Particle B). More specifically, the dust suppressing agent comprising polyurethane of Examples V-X encapsulates the Core Particle B and prevents dust formation upon mechanical abrasion, as indicated by the low dust values and the high dust reduction gradient values for Examples V-X. Further, the dust suppressing agent comprising polyurethane does not significantly inhibit or prevent the dissolution of the Core Particle B, as indicated by the low dissolution gradients.

It is to be understood that the appended claims are not limited to express and particular compounds, compositions, or methods described in the detailed description, which may vary between particular embodiments which fall within the scope of the appended claims. With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, it is to be appreciated that different, special, and/or unexpected results may be obtained from each member of the respective Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims.

It is also to be understood that any ranges and subranges relied upon in describing various embodiments of the present invention independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the enumerated ranges and subranges sufficiently describe and enable various embodiments of the present invention, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range “of from 0.1 to 0.9” may be further delineated into a lower third, i.e., from 0.1 to 0.3, a middle third, i.e., from 0.4 to 0.6, and an upper third, i.e., from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as “at least,” “greater than,” “less than,” “no more than,” and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of “at least 10” inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. Finally, an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range “of from 1 to 9” includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1, which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described. 

What is claimed is:
 1. A dust suppressing aggregate comprising: A. a core particle; and B. a dust suppressing agent disposed about said core particle and comprising polyurethane for suppressing dusting of said core particle; wherein said dust suppressing aggregate has a dust reduction gradient of greater than 20% and a dissolution gradient equal to or less than 30 after 1 day of aging in water at 38° C.
 2. A dust suppressing aggregate as set forth in claim 1 wherein said polyurethane is present in an amount of from 0.3 to 5.5 parts by weight based on 100 parts by weight of said core particle.
 3. A dust suppressing aggregate as set forth in claim 2 having a dust reduction gradient of greater than 60%.
 4. A dust suppressing aggregate as set forth in claim 3 having a dissolution gradient equal to or less than 15 after 1 day of aging in water at 38° C.
 5. A dust suppressing aggregate as set forth in claim 1 wherein said polyurethane comprises the reaction product of an isocyanate component and a polyol component.
 6. A dust suppressing aggregate as set forth in claim 5 wherein said polyol component comprises a high molecular weight (HMW) polyol having a nominal functionality of at least 2.5 and a hydroxyl number of from 20 to 300 mg KOH/g.
 7. A dust suppressing aggregate as set forth in claim 6 wherein said HMW polyol has a viscosity at 25° C. of from 100 to 2000 cps.
 8. A dust suppressing aggregate as set forth in claim 5 wherein said polyol component comprises a catalytic polyol different than said HMW polyol and derived from an amine-based initiator.
 9. A dust suppressing aggregate as set forth in claim 5 wherein said isocyanate component comprises polymeric diphenylmethane diisocyanate and has an NCO content of about 31.5 weight percent.
 10. A dust suppressing aggregate as set forth in claim 5 wherein said isocyanate component and said polyol component are reacted at an isocyanate index of from 90 to
 160. 11. A dust suppressing aggregate as set forth in claim 1 wherein said core particle comprises a fertilizer.
 12. A dust suppressing aggregate as set forth in claim 1 wherein said core particle comprises monoammonium phosphate and/or urea.
 13. A method of forming a dust suppressing aggregate including a core particle and a dust suppressing agent comprising polyurethane and disposed about the core particle for suppressing dusting of the core particle, said method comprising the steps of: A. providing the core particle; and B. encapsulating the core particle with the polyurethane to form the dust suppressing aggregate having a dust reduction gradient of greater than 20% and a dissolution gradient equal to or less than 30 after 1 day of aging in water at 38° C.
 14. A method as set forth in claim 13 wherein the polyurethane is present in an amount of from 0.3 to 5.5 parts by weight based on 100 parts by weight of the core particle.
 15. A method as set forth in claim 14 wherein the dust suppressing aggregate has a dust reduction gradient of greater than 60%.
 16. A method as set forth in claim 15 wherein the dust suppressing aggregate has a dissolution gradient equal to or less than 15 after 1 day of aging in water at 38° C.
 17. A method as set forth in claim 13 wherein the step of encapsulating the core particle with the polyurethane is further defined as reacting an isocyanate component and a polyol component to form the polyurethane.
 18. A method as set forth in claim 17 wherein the polyol component comprises a high-molecular weight (HMW) polyol having a nominal functionality of at least 2.5 and a hydroxyl number of from 20 to 300 mg KOH/g.
 19. A method as set forth in claim 18 wherein the polyol component further comprises a catalytic polyol different than the HMW polyol and derived from an amine-based initiator.
 20. A method as set forth in claim 17 wherein the isocyanate component comprises polymeric diphenylmethane diisocyanate and has an NCO content of about 31.5 weight percent.
 21. A method as set forth in claim 17 further comprising the step of heating at least one of the core particle, the isocyanate component, and the polyol component to a temperature greater than 40° C. prior to or simultaneous with the step of mixing the isocyanate component and the polyol component.
 22. A method as set forth in claim 17 wherein the isocyanate component and the polyol component are reacted at an isocyanate index of from 90 to
 160. 23. A method as set forth in claim 13 wherein the core particle comprises a fertilizer.
 24. A method as set forth in claim 13 wherein the core particle comprises monoammonium phosphate and/or urea.
 25. A system for producing a dust suppressing aggregate including a core particle and a dust suppressing agent comprising polyurethane and disposed about said core particle for suppressing dusting of said core particle, the polyurethane present in an amount of from 0.3 to 5.5 parts by weight based on 100 parts by weight of said core particle and comprising the reaction product of an isocyanate component and a polyol component, said system comprising: A. said isocyanate component; B. said polyol component reactive with said isocyanate component for producing the polyurethane; and C. said core particle; wherein said dust suppressing aggregate has a dust reduction gradient of greater than 20% and a dissolution gradient equal to or less than 30 after 1 day of aging in water at 38° C.
 26. A system as set forth in claim 25 wherein said dust suppressing aggregate has a dust reduction gradient of greater than 60%.
 27. A system as set forth in claim 26 wherein said dust suppressing aggregate has a dissolution gradient equal to or less than 15 after 1 day of aging in water at 38° C.
 28. A system as set forth in claim 25 wherein said polyol component comprises a high-molecular weight (HMW) polyol having a nominal functionality of at least 2.5 and a hydroxyl number of from 20 to 300 mg KOH/g.
 29. A system as set forth in claim 25 wherein said core particle comprises a fertilizer. 